1. Field of the Invention
The present invention relates to a motorcycle that includes a unit-swing type, rear wheel driving power unit, and rear suspension units on both right and left sides of the rear wheel.
2. Description of Related Art
A unit-swing type, rear wheel driving power unit is now widely used in scooter type motorcycles. In such a motorcycle having this unit-type, rear wheel driving power unit, a front side portion of a power unit including an engine and a transmission mechanism is supported by a vehicle body frame for swinging in a vertical direction. A rear wheel is mounted on a rear wheel axle projecting from a rear end side portion of the power unit. Respective top ends of a right and left pair of rear suspension units are coupled with both upper right and left portions of a rear end of the vehicle frame. A bottom end of one rear suspension unit is coupled with a housing of the power unit, while a bottom end of the other suspension unit on the opposite side is coupled with the rear wheel axle via a bearing or a rear arm, which supports the rear wheel axle, via a bearing. Also, in this kind of scooter type motorcycle, generally, a muffler is disposed on a side portion of the rear wheel on the side opposite the side on which the power unit is disposed.
In this kind of conventional motorcycle, generally, a number of structures have an arrangement in which the respective rear suspension units on both the right and left sides extend parallel to each other and are positioned at the same height as one another so that the rear suspension units overlap with each other in a side view.
Also, in other examples, the respective right and left rear suspension units have different heights from each other (for example, see Patent Documents 1, 2 and 3). That is, instead of the relationship in which the bottom end of one rear suspension unit is coupled with the housing of the power unit while the bottom end of the other rear suspension unit is directly coupled with the rear wheel axle via the bearing, the coupling position of the bottom end of the rear suspension unit on the power unit side is higher than the coupling position of the bottom end of the rear suspension unit on the opposite side.
Further, in some other examples, respective axis lines of the right and left rear suspension units are shifted from each other in a fore to aft direction (for example, see Patent Document 4).
Patent Document 1 is Japanese Utility Model Publication No. Hei 1-39672; Patent Document 2 is Japanese Utility Model Publication No. Hei 1-36710; Patent Document 3 is Japanese Utility Model Publication No. Hei 2-07117; and Patent Document 4] is Japanese Patent No. 2710982.
However, in all of the prior art, the rear suspension unit positioned on the side opposite the side on which the power unit is disposed is lower than the other rear suspension unit. Although this is not so serious a problem with a small size scooter, it can be a problem with a large size scooter because of the inconvenience in exchanging tires.
That is, in connection with a motorcycle having this kind of unit-swing type, rear wheel driving power unit on one side of the rear wheel in a transverse direction, the rear wheel is exchanged for a new one generally on the side opposite the side on which the power unit is disposed(i.e., opposite power unit side). In such a configuration, because the rear suspension unit is positioned on the side of the rear arm where the exchange work is made, the rear suspension unit can disturb the work. Normally, the top end of the rear suspension unit is coupled with the rear portion of the vehicle body frame, while the bottom end thereof is coupled with the axle via a bearing or is coupled with the rear arm, which supports the rear wheel axle, by a pin. Thus, in order to exchange the rear wheel with a new one, the lower end of the rear suspension unit needs to be lifted up rearward.
However, when the rear suspension unit on the opposite power unit side is positioned at the same height as the rear suspension unit on the power unit side or is positioned lower than it, the lower end of the suspension unit needs to be lifted up on a large scale, or sufficent space for exchanging tires cannot be ensured. Workability can be bad, accordingly. Particularly, in a large size scooter, a vehicle body cover is likely to cover the rear wheel and components around it, including the rear suspension unit, because of design requirements. This makes it difficult to lift up the bottom end of the rear suspension unit on a large scale and further worsens workability.